Battery Energy Storage Systems (BESS) play a fundamental role in energy management, providing solutions for renewable energy integration, grid stability, and peak demand management. In order to effectively run and get the most out of BESS, we must understand its key components and how they impact the system’s efficiency and reliability.
Get battery analytics trends and industry knowledge delivered directly to your inbox. Because we batteries.
BESS consists of many battery cells connected in serial and/or parallel connections. A parallel connection of battery cells forms a logical cell group, and these groups are then connected in series. The connected battery cells and the BMS, sometimes with a PCS, form battery modules. Several modules create a battery rack, and multiple racks are connected to form battery banks or arrays, constituting the battery side of the system. Figure 0 depicts the configuration of a BESS rack.
The configuration of these connections—whether series or parallel—determines the BESS’s voltage, capacity, and overall performance. This configuration is crucial for the optimal operation of the system and significantly impacts its efficiency and lifespan.
The differences between serial and parallel connections of batteries reveal distinct advantages and disadvantages associated with each configuration.
Advantages: Increase voltage, reducing losses and potentially reducing inverter costs. Lower currents for the same power lead to reduced losses, allowing the use of smaller cables and power electronics, which lowers costs.
Disadvantages: Disadvantages: The overall performance is determined by the weakest cell. If one cell reaches 0% State of Charge (SOC), discharge must stop for the entire series connection to avoid deep discharging the weak cell.
Advantages: Increase current or capacity, reducing BMS costs due to fewer logical cells to monitor. Lower voltage levels reduce electrical shock risks, and parallel cells can support each other, minimizing the impact of a weak cell.
Disadvantages: Require larger cables to handle higher currents, leading to increased losses and heat generation. The current flowing between cells cannot be controlled, posing a safety risk if one cell short circuits. Current interruption devices (CIDs) are needed to prevent this.
Figure 1 summarizes the advantages and disadvantages of serial and parallel-connected battery cells.
Conclusion
Understanding the key components of BESS and the significance of battery connections helps stakeholders manage and optimize these systems and realize their impact on the economic health of their assets. In BESS mainly serial connections of battery cells are used. In a serial connection, the weakest cell determines the performance of the entire serial string. Factors such as manufacturing spreads, imbalances, and varying aging rates contribute to differences in battery cells connected in serial. This highlights the need for efficiency gains in high-voltage systems through cost reduction associated with cables and minimizing losses.
Dr. Georg Angenendt is a scientist and entrepreneur with expertise in mobility and utility-scale battery energy storage systems (BESS). His research on testing, modeling, commissioning, and optimization of battery storage systems has been published in international journals and at conferences. Since 2020, he is the Chief Technology Officer at ACCURE Battery Intelligence, developing advanced analytics software to help companies assess battery risk, ensure safety, and maximize asset value. His personal passion is Martial Arts: mixed martial arts, luta livre, grappling, boxing and Brazilian jiu-jitsu.
ACCURE helps companies reduce risk, improve performance, and maximize the business value of battery energy storage. Our predictive analytics solution simplifies the complexity of battery data to make batteries safer, more reliable, and more sustainable. By combining cutting-edge artificial intelligence with deep expert knowledge of batteries, we bring a new level of clarity to energy storage. Today, we support customers worldwide, helping optimize the performance and safety of their battery systems. Visit us at accure.net.